Multiple electrode discharge tube energizing



March 17,'1936. B. F, MlEssNER MULTIPLE ELECTRODE DISCHARGE TUBE ENERGIZING 3 Sheets-Sheet 1 Original Filed Sept. 18, 1929 F f z,

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B. F. MlEssNER 2,034,663

MULTIPLE ELECTRODE DISCHARGE TUBE ENERGIZING Original Filed Sept. 18, 1929 3 Sheets-Sheet 2 )VULT PLATE PUTE/VT//IL HUM //v Qu/vAu-A/r' A lc' Voz ms CA PA c/ rf 0F Co/vaA-Msfe @www March 17, 1936. FA MIESSNER 2,664,663

MULTIPLE ELECTRODE DISCHARGE TUBE ENEBGIZING Original Filed Sept. 18, 1929 3 51198105-5116 3 Patented Mar. 17, 1936 UNITED STATES PATENT OFFICE MULTIPLE ELECTRODE DISCHARGE TUBE ENERGIZING Delaware Application September 18, 1929, Serial No. 393,387 Renewed January 27, 1934 17 Claims.

My invention relates to energizing multiple electrode electron discharge tubes and like space discharge devices for operation from unsteady sources of current energy so as to limit, control, or neutralize the eiects of the unsteady current energizing, and in particular to avoid hum production in systems employing such tubes for amplifying sound representing currents. radio broadcast receivers and electrical phonographic reproducers in particular being contemplated.

My present invention relates to the control of the various phenomena accompanying the operation of the system disclosed in Fig. 3 of my copending application Serial Number 360,045 led May 3, 1929, with varied constants and circuit connections, and includes modifications thereof, so that this application is a continuation in part of my application hereinbefore mentioned.

My present invention has for a particular object hum current suppression or control in the output circuit of a vacuum tube with the aid of I an auxiliary electrode, such as an electrode positioned between the cathode and anode and controlling the potential of the auxiliary electrode relative to the cathode in two respects, namely, with respect to the direct current component of a fluctuating unidirectional energizing source, and with respect to the fluctuating current component of said source.

Another object is the suppression or control of carrier current modulation in so-called radio frequency ampliers arising from energizing the electrodes of the tubes of such amplifiers from unsteady sources of current.

My invention is particularly applicable to systems employing the so-called shielded-grid type of tube having the electrodes energized with energy derived from an alternating current source of supply.

Other objects and features of my present invention will be apparent from the following description and explanation in connection with the gures of the accompanying drawings in which like reference characters designate like elements so far as possible in the several figures in which:

Fig. 1 diagrammatically illustrates a four elelment electron discharge tube of the so-called shielded grid type connected in a system for describing and explaining the eiects of the energization of the electrodes of the tube in accordance with the principles of my invention, and particularly suited for analyzing the eects within the tube when the anode or plate thereof is energized by fluctuating potentials while the shielding electrode is energized either from a source (Cl. Z-27) of non-uctuating potential or from a source of fluctuating potential similar to the plate energization.

Fig. 2 diagrammatically illustrates a system utilizing features of Fig. 1 and wherein the tube VT is used as a filter device similar to the use of the tube described in my copending application Serial Number 360,042 filed May 3, 1929.

Fig. 3 diagrammatically illustrates another system utilizing features of Fig. 1 in which the load 10 upon the source of uctuating current is reduced to a minimum by the omission of loss-resistors, and including distribution of filtering devices within the system where needed, the basis for which two features may be found in my copend- ,15 ing application Serial Number 117,076, filed June 19, 1926.

Fig. 4 illustrates a modification of the system of Fig. 3 wherein residual fluctuations derived from the plate current of the tube are impressed 20 upon the input circuit thereof of such phase and intensity to oppose, for obliteration if desired, any hum currents tending to pass through the output transformer.

Fig. 5 diagrammatically illustrates the system 25 of Fig. 3 energized by the system of Fig. 2 and wherein the arrangement constitutes two stages of amplification in cascade, one stage acting as an output stage and also as a filter system for the preceding stage of amplication, similar to 30 the arrangement illustrated and described in Fig. 2 of my copending application 360,042 hereinbefore mentioned.

Figs. 6, 7, 8, 9 and 11 are graphs illustrating the logical development of a theoretical basis for the present invention.

Fig. 10 is a modification of the system shown in Fig. 4.

Referring to Figs. 1 to 5 SF indicates a source of fluctuating unidirectional current, shown in 0 Fig. 1 with the usual conventional details for deriving such current from an alternating current source, and conventionally in Figs. 2 to 5. The negative and positive terminals I, 2 respectively, are shown shunted by the usual storage and lter condenser C1, which may be followed by additional filter elements of well-known selection and arrangement if desired. VT is shown for example as the four electrode so-called shielded-grid type of tube, a commercial type 324 for 50 example, which may have a unipotential cathode K maintained at effective electron emission temperature by heating the element H with alternating current supplied through a transformer HT. The plate electrode of each tube is energized by connection to the positive terminal 2 of source SF.

In the systems of Figs. 1, 3, 4 and 5, I have provided a resistance R connected between the cathode K and the negative terminal I of source SF for developing the usually required negative grid potential, the grid G of each tube being connected to a point in R more negative than cathode K through an input system, for example a transformer T1 suitable for the current frequencies being handled. The resistance R may be bypassed by the usual signal current by-pass condenser C2. Each of the systems is provided with an output transformer T2 suitable for the frequency of the currents being handled, though input and output elements other than transformers may be employed as is well known.

In the arrangement of Fig. 1, I have shown various switches for arriving at selected circuit connections and selected modes of energizing the cold electrodes of the tube VT to facilitate explaining the features of my invention in connection with effects had and graphic representations of them. The battery B1 with associated potentiometer P3 provides for impressing any desired degree of steady potential of auxiliary electrode G' through switch SW2, and the potentiometer P2 across the iiuctuating current course permits of substituting a fluctuating potential for the steady battery potential. The potentiometer P1 permits of energizing the plate electrode P with any desired degree of fluctuating potential. The switch SW1 permits of introducing or removing a resistance R1 of any desired value from a series relation with auxiliary electrode G. Switch SW3 permits of connecting a. condenser C3 of any desired value between the auxiliary electrode G' and either the cathode K or the negative terminal l of the source. Switch`SW4 provides. for short-circuiting or removing any effects of potential in resistance R from grid electrode G.

In general practice with amplifying tubes energized from alternating current sources it is desirable to materially diminish, or to limit and control in specific manner, the fluctuating current component derived from such energizing appearing across transformer AT2 or other output element if acceptable hum reduction is to be had. By pointing out different connections possible in Fig. 1 and the results had as shown in the graphs of Figs. 6, '7, 8 and 9, I believe I develop logically a theoretical basis for an understanding of my present invention.

With switch SW4 closed to remove potential effects from the grid G, plate P and auxiliary electrode G energizing effects can be examined independently of grid potential effects. Now the battery B1 steadily maintaining G at a usual operating potential of approximately 50 volts through left hand closure of switch SW2, and switches SW1 and SW3 being open or closed as not affecting direct current energizing, obviously no hum current production arises from auxiliary electrode energizing, thus leaving the arrangement in condition for investigating the hum current production arising from plate electrode Ps energizing with fluctuating currentY through potentiometer P1, and this is shown in the graphs of Fig. 6 as representative of one set of measurements made by me when employing a source of fluctuating potential having an average direct current potential of 220 volts between terminals l and 2 and a severe fluctuating component of 20 volts.

Thus connected and energized the average plate current changed as shown in graph Ip of Fig. 6 as the plate potential was changed as indicated by the abscissae scale. Voltmeter readings of equivalent hum current volts in indicator HI produced the hum graph En of Fig. 6 with the changing of plate potential.

Analyzing these graphs it is seen that in that region where the plate current graph is steep the hum production is severe, but falls off materially beyond the indicated point O of plate current saturation, becoming in fact most reasonably low as the plate current graph flattens out. In other words, as far as hum production arising in plate energizing with fluctuating current is concerned, the proper point of operation for materially reducing hum is beyond the origin of saturation O.

The next step investigates the effect had by energizing the auxiliary electrode G' with the same iiuctuating potential by connecting switch SW2 to potentiometer P2 to give approximately 50 volts as before, switch SW1 to eliminate resistance R1 and switch SW3 open to eliminate condenser C3, switch SW4 still being closed.

'Ihe result is shown in the graphs of FigQ'I, the hum graph E11 showing that the hum current in indicator I-II increases rapidly at the steep part of the plate current graph Ip, and remains at a slightly increasing largevalue beyond the origin of saturation O, substantially the same configuration as the plate current graph. Comparing with the graphs of Fig. 6, it is seen that a fluctuating potential on the auxiliary electrode has an effect on hum production many times more troublesome than such a potential on the plate when beyond saturation. I also point out that in the region indicated by the dotted portion :r to y of graph E11 of Fig. 7 there is noted a decided tendency towards instability analogous to high frequency oscillation due to so-called dynatron effect.

These considerations therefore point out the particular desirability of materially reducing the effect of energizing the auxiliary electrode G with fluctuating potential current, and I have found that the usual system permits of accomplishing this in a simple and effective manner. Usually 'the potential of the source SF for the plate electrode is much in excess of that needed for the auxiliary electrode, so that an excess potential selected from potentiometer P2, or even from the positive terminal 2, can be reduced by the loss of potential in a high resistance R1 had when switch SW1 is open or eliminating it entirely. Selecting a definite value of resistance R1 for a given potential from P2 will result in the desired operating potential on G as determined by the space current flow from cathode K to auxiliary electrode G', and with the usual high potential of source SF for the plate electrode the resistance R1 can be made high; that is, of the order of 100,000 ohms to produce the desired lowering of potential on G.

This order of high resistance is particularly suitable for co-operating with a suitable value condenser C3, as by closing switch SW3, for most effectively filtering the usual 60 or 120 cycle fluctuating current originating in source SF from rectified commercial `alternating current, thereby materially reducing the fluctuating potential component on auxiliary electrode G', even though the filtration of the fluctuating current at the source SF is most incomplete.

Y The effect of this high order of filtration of the energy applied to electrode G in company -with normal fluctuating energy applied to the plate electrode is shown in the graphs of Fig. 9, switch SWi still being closed to eliminate grid effects. As before graph Ip shows the plate current with change of plate potential, the potential of electrode G being maintained unchanged. Graph Eh represents the degree of hum current for various values of plate potential as observed in indicator HI, and shows a most favorable low degree of hum beyond origin of saturation O.

While the preceding considerations provide for definite steps of improvement, further benefits can be had by bringing into cooperation grid. effects. With switch SW4 open so that iiuctuations passing through grid biasing resistance R are impressed on grid G, the graphs of Fig. 8 illustrate these effects. With switch SW3 closed to the right so that fluctuating current components passing through condenser C3 do not pass through resistance R to effect fluctuating potential on grid G hum improves with increase of capacity of condenser C3 as shown by graph a., which is substantially linear, indicating that the improvement is due to improved filtration of the iiuctuating component or auxiliary electrode G' almost entirely.

With switch SW3 closed to the left, so that fluctuating current passing through condenser C3 also passes through resistance R to affect grid G, graph b of Fig. 8 shows the resulting hum change withv change of Value of condenser C3. Here the hum falls off sharply with increase of capacity of C3, becoming a minimum in the particular arrangement investigated with a capacity of C3 substantially .3 microfarads, land increasing thereafter. This therefore shows that a controlled amount of hum feed-back is useful to oppose by grid effects the hum arising from energizing the plate and auxiliary electrodes from fluctuating potential sources. The plate and ,auxiliary electrode effects are in the same phase, so that they cannot be used one against the other for neutralizing effect.

I also point out that the use of a high resistance R1 in series with the auxiliary electrode has the benefit of eliminating the unstable condition indicated from :z: to y in graph E11 of Fig. 'l previously mentioned.

Fig. 2 shows one arrangement for employing some of the features of my invention outlined in connection with Fig. 1. Four electrode tube VT is energized from the fiuctuating and poorly filtered output of source SF. All loss-resistors are eliminated to lessen current drain on the source and filter, thereby having best filtration possible for the filter material used. The reduced potential of auxiliary electrode G is obtained by lowering the potential of the source through high resistance R1 series connected, the fiiter condenser C3 being connected between electrode G' and cathode K as previously described. 'I'he grid G and cathode K are tied together.

With this arrangement of Fig. 2 the potential developed across load resistance LR, shunted by by-pass condenser BC, is substantially steady as shown by graph En in Fig. 9, so that this system may be used in lieu of the system shown in Fig. 1 of my copending application Serial Number 360,042 iiled May 3, 1929 for the energization of the space discharge paths of other tubes of a radio receiving system or any other device in which a unidirectional current of steady potential is desired.

Fig. 3 illustrates the hum feed-back system described with reference to Fig. l with the additional feature that in this instance the load of the loss resistor has been removed from the filter circuit and the electrode G' is energized directly from the positive terminal 2 of the source SF. This arrangement shown in Figs. 2 and 3 permits of appreciable reduction of the values of the elements of the filter system to such an extent that a single condenser of a Value of approximately 2 microfarads shunting the output of a full wave rectifier constitutes a sufiicient lter system in many instances.

Figure 4 diagrammatically illustrates another system specifically described with reference to Fig. l with the added feature that condenser C5 is utilized as a hum feed-back control. The use of such a condenser has been described in detail with reference to a three element tube in my copending application Serial Number 251,807 filed Feb. 4, 1926 and this circuit arrangement is substantially the same as that of Fig. 3 of my copending application Serial Number 360,045 filed May 3, 1929.

Summarizing briefly, condenser C5 of Fig. 4 shunts a portion of the hum currents from the space discharge path of the tube directly to resistance R, and permits by selection of capacity values developing hum potentials across resistance R in the grid-filament circuit of the tube of such phase and amplitude that the effect on the grid Gis controlled to most effectively commutate from the space discharge path of the tube any hum currents tending to develop therein by reason of the liuctuating potential upon the plate and auxiliary electrodes.

Fig. 5 diagr'ammatically illustrates a tube VT1 associated with circuits in the manner of Fig. 3 energized through a tube system like that of Fig. 2 including a tube VTz, with the additional feature that the tube VTz is utilized also as a stage of amplification succeeding the tube VT1. In this arrangement the signal input of the system is through the transformer T1, and the output of the system is through the transformer condenser systern TC, the grid-filament circuit of tube VTz being coupled to the plate circuit of tube VT1 through the transformer T2. l

In Fig. l0, I have shown a modification of thc system of Fig. 4 in that I have provided condenser C4 and resistance R4 to function as a hum feedback element for developing neutralizing potentials across the resistance R for grid G. In this arrangement I have provided switches SW5 and SW6 to enable a more clear understanding of the operating characteristics of this circuit as graphically illustrated by the graphs of Fig. 11.

By way of example, with a tube of the 324 type, resistance R of 2000 ohms, a potential across condenser C1 of 250 volts direct current having a fluctuating component of 20 volts, and switches SW5 and SW6 open, the resistance R1 was varied between zero and 100,000 ohms to obtain the hum potentials in millivolts represented by graph A of Fig. 11, a most excessive order of hum.

With switch SW5 closed and a condenser at C3 of .25 microfarads, the graph B of Fig. 11 graphically illustrates the hum in millivolts as the resistance R1 varied between zero and 100,000 ohms.

Comparison of graphs A and B with the aid of the hum millivolt ordinates at the left of Fig. 11 shows the effectiveness of filtration in the auxiliary electrode circuit on hum reduction.

Further, closing switch SW6 and for each value F resistance R1 is varied between zero and 100,000 ohms.

A comparison of graphs B, using ordinates at the left of the figure, shows the effectiveness of selected hum feed-back control in such a circuit. A comparison of graphs A, ordinates at left, and C ordinates at right, shows the effectiveness of hum elimination when filtration and hum feedback are combined, the importance of such comparison being overwhelming when it is considered that the fluctuating component of the potential across the output of the filter is substantially ten percent of the aggregate potential and the resultant hum is substantially one millivolt.

The systems shown and described are not only of value for the audio frequency portion of radio receivers when energizing a so-called all-electric radio receiver from commercial alternating current supply, but of great importance to the stages of radio frequency amplification as well.

It is well known that the energizing of tubes in the radio frequency portion from unsteady sources of potential results in modulation of the incoming high frequency carrier currents, and that variations in the plate circuits of such tubes are more effective than grid circuit variations, so-called plate modulation being generally used in preference to so-called grid modulation in transmitting systems for this reason.

The energizing modulation is effectively transferred with the carrier current from stage to stage to be nally liberated in the detector as a source of hum for amplification in the audio frequency portion of the receiver often developing a most disagreeable order of hum.

It is appreciated from graph B of Fig. 11 that mere effective filtration of the shielding grid circuit is most effective in reducing plate circuit hum variations, and since grid variations are not effective modulators, it in general Suices in treating radio frequency stages to rely on filtration without bringing in the Vernier improvement of hum feed-back shown by graph C of Fig. 11. This refinement is particularly helpful in audio frequency stages followed by one or more stages of amplification.

Having described my invention with respect to several specific circuits and combinations thereof it is apparent that various modifications thereof may be made therein without departing from the spirit of my invention as defined in the claims appended hereto.

I claim:

1. In an electrical system, the combination of a source of unidirectional fluctuating current, an

electron tube having a cathode, grid, auxiliaryelectrode and plate, means for energizing the space discharge paths of said tube between said cathode, grid and plate from said source, means for determining the direct current potential of said auxiliary electrode at a potential intermediate the direct current potentials of said cathode and plate electrode, means for reducing the fluctuating current component of the potential applied to said auxiliary electrode more nearly to the fluctuating component existing at said catliode, and means for impressing a predetermined amount of the fluctuating current potential of said source upon the grid of said tube of a phase to neutralize within said tube the effect of the fluctuating current energization of the electrodes of said tube.

2. In an electrical system, the combination of a Source of unidirectional fluctuating current, an electron tube having a cathode, grid, auxiliary electrode and plate, means for energizing the space discharge paths of said tube between said cathode, grid and plate from said source, means for determining the direct current potential of said auxiliary electrode at a potential intermediate the direct current potentials of said cathode and plate electrodes whereby said electron tube is operating at a point in the substantially flat portion of its plate current-plate potential curve, means for reducing the fluctuating current component of the potential applied to said auxiliary electrode more nearly to the fluctuating component existing at said cathode, and means for impressing a predetermined amount of the fluctuating current potential of said source upon the grid of said tube of a phase to neutralize within said tube the effect of the fluctuating current energization of the electrodes of said tube.

3. In an electrical system, the combination of a source of unidirectional fiuctuating current, an electron tube having a cathode, grid, auxiliary electrode and plate, means for energizing the space discharge paths of said tube between said cathode, grid and plate from said source, means for determining the direct current potential of said auxiliary electrode at a potential intermediate the direct current potentials of said cathode and plate electrode, and means for reducing the fluctuating current component of the potential applied to said auxiliary electrode more nearly to the fluctuating component existing at said cathode, said means including a high impedance connection between said auxiliary electrode and said plate energizing means, and a connection between said auxiliary electrode and the cathode of said tube of low impedance to the fluctuating component of said source, and means for impressing a predetermined amount of the fluctuating current potential of said source upon the grid of said tube of a phase to neutralize within said tube the effect of the uctuating current energization of the electrodes of said tube.

4. In an electrical system, the combination of a source of unidirectional fluctuating current, an electron tube having a cathode, grid, auxiliary electrode and plate, means for energizing the space discharge paths of said tube between said cathode,v grid and plate from said source, means for determining the direct current potential of said auxiliary electrode at a potential intermediate the direct current potentials of said cathode and plate electrodes, means for reducing the fluctuating current component of the potential applied to said auxiliary electrode more nearly to the fluctuating component existing at said cathode, said means including a high impedance connection between said auxiliary electrode and said plate energizing means and a capacity connection between said auxiliary electrode and the cathode of said tube, said capacity connection being of low impedance to the fluctuating current component of said source, and means for impressing a predetermined amount of the fluctuating current potential of said source upon the grid of said tube of a phase to neutralize within said tube the effect of the fluctuating current energization of the electrodes of said tube.

5. In an electrical system, the combination of a source of unidirectional fluctuating current, an electron tube having a cathode, grid, auxiliary electrode and plate, means for energizing the space discharge paths of said tube between said cathode, grid and plate from said source, means for determining the direct current potential of said auxiliary electrode at a potential intermediate the direct current potentials of said cathode and plate electrode whereby said electron tube is operating at a point in the substantially iiat portion of its plate current-plate potential curve, means for reducing the uctuating current component of the potential applied to said auxiliary electrode more nearly to the fluctuating component existing at said cathode, said means including a high impedance connection between said auxiliary electrode and said plate energizing means and a capacity connection between said auxiliary electrode and the cathode of said tube, said 'capacity connection being of low impedance to the fluctuating current component of said source, and means for impressing a predetermined amount of the fluctuating current potential of said source upon the grid of said tube of a phase to neutralize within said tube the effect of the fluctuating current energization of the electrodes of said tube.

6. In an electrical system, the combination of a source of energy, an electron tube having a cathode, grid, auxiliary electrode and plate, means for energizing the space discharge paths of said tube between said cathode, grid and plate, a high impedance connection between said auxiliary electrode and one terminal of said source, a condenser connected between said auxiliary electrode and a point having a potential not greatly differing from the potential of the other terminal of said source, said impedance and condenser having such electrical dimensions as to constitute an effective filter for audio frequency currents, and means for impressing a uctuating potential upon the grid of said tube of a phase to commutate out the fluctuating component of the plate current of said tube.

7. In an electrical system including an electron tube having a cathode, grid, auxiliary electrode and plate and connections for energizing the cathode plate discharge path of said tube from a source of unidirectional pulsating current, the method of eliminating fluctuations in the space current of said tube due to the fluctuating current energization which consists in energizing the auxiliary electrode with a substantially nonfluctuating potential of a value such that said tube operates at a point above the origin of saturation in the plate current plate potential curve of said tube and impressing upon the grid of said tube a fluctuating potential of such' phase and amplitude as to substantially neutralize within said tube the residual fluctuations in the space discharge current of said tube.

8. In an electrical system, the combination of a source of energy in which there exists an undesired fluctuating component, an electron tube having a cathode, grid, auxiliary electrode and anode, means for energizing the space paths of said tube, a high impedance connection between said auxiliary electrode and one terminal of said source, a capacity connected between said auxiliary electrode and a point having a potential not greatly differing from the potential of the other terminal of said source, said impedance and capacity having such electrical dimensions as to constitute an effective filter for audio frequency currents, a biasing resistance connected between said cathode and grid, and means for shunting through said biasing resistance a portion of the undesired fluctuating component of such phase and magnitude that effects of the fluctuating component upon the tube are substantially neutralized.

9. In an electrical system the combination of a source of energy in which there exists an undesired fluctuating component, an electron tube having a cathode, a grid, an auxiliary electrode and an anode, means comprising said source for energizing the space paths of the tube, a connection including a high impedance between the auxiliary electrode and one terminal of the source, a capacity connected between the auxiliary electrode and a point having a potential not greatly differing from the potential of the other terminal of the source, said impedance and capacity comprising virtually a shunt circuit across the source, the electrical dimensions of which are such as to simulate, in eifect, an audio frequency by-pass circuit, a biasing impedance connected between the cathode and grid, an anode cathode circuit including said source and the biasing impedance in series, and means for impressing across the biasing resistance a portion of the undesired iluctuating component derived from the source in such phase and magnitude that the effects of the undesired fluctuating component upon the tube are minimized.

10. In an electrical system the combination of a source of unidirectional uctuating current, an electronic tube including an indirectly heated cathode, a signal grid, an auxiliary grid and an anode, a connection from the signal grid to the negative side of said source including a coupling means, a connection from the negative side of said source to the cathode including a bias resistor, means including a coupling element connecting the anode to the positive side of said source, a connection from the positive side of said source to the cathode end of the bias resistor including an impedance and a condenser in series, a connection from the auxiliary electrode to the junction point of said serially arranged impedance and condenser circuit, said last named condenser being proportioned so that hum frequencies are transferred from the positive side of said source to the negative side of said source through the bias resistor and a by-pass condenser shunted across the bias resistor.

11. In an electrical system the combination of a source of energy, an electron tube having a cathode, a signal grid, an auxiliary electrode and an anode, means for energizing the space discharge paths of said tube between the cathode, grid and plate, a connection having a resistance of the order of 100,000 ohms between the auxiliary electrode and the positive side of said source, a connection including a variable condenser between the auxiliary electrode and the negative side of said source, said resistance and last named condenser being proportioned with respect to the fluctuating component of the source so that they form a shunt circuit across the source which acts, in effect, to by-pass hum frequencies from one side of the source to the other.

12. In a system as described in claim 11 in combination with said source of energy a lter circuit comprising at least a condenser shunted across the source for filtering out at least a portion of the fluctuating component of the energy from the source.

13. In an electrical system the combination of a source of unidirectional fluctuating current, a filter circuit connected tothe output of said source comprising at least a condenser shunted across the source, a space discharge tube provided with a cathode, a signal grid, an auxiliary grid and an anode, means for energizing the space discharge paths of said tube between said cathode, grids and anode from said source, means for determining the direct current potential ofthe auxiliary grid at a potential intermediate the direct current potentials of said cathodeV and anode, means for reducing the fluctuating current componentof the potential applied to said auxiliary grid more nearly to the uctuating component existing at said cathode, said means comprising a connection between the auxiliary grid and the cathode for maintaining both thereof at substantially the same alternating current potential, and means including the last named means for impressing a predetermined amount of the iiuctuating current potential of said source upon the signal grid of said tube of a phase to neutralize within the tube the `effect of the fluctuating current energy of the electrodes of said tube.

14. In an electrical system the combination of a source of unidirectional fluctuating current a filter circuit therefor for ltering out a substantial portion of the fluctuating component of the current from said source, the output of the lter circuit including a negative and a positive terminal, an electron tube having a cathode, a grid, an auxiliary electrode and a plate, a connection from the plate electrode to the positive terminal of the filter output including a coupling element, a connection including another coupling element from the grid of the tube to the negative terminal of the lter circuit, a bias resistor connected from the negative terminal of the iillter to the cathode of the tube, said bias resistor being included'in both the grid circuit of thev plate circuit of the tube, means for determining the direct current potential of the auxiliary electrode so that the auxiliary electrode will be maintained at a potential intermediate the direct current potentials of the cathode and plate Yelectrodes whereby said electron tube is constrained to operate at a point in the substantially at portion of its plate current, plate potential characteristic curve, means for reducing the fluctuating current component of the potential applied to the auxiliary electrode more nearly to the iluctuating component existing at said cathode comprising an alternating current connection between the auxiliary electrode and the cathode and means including the last named means for impressing a predetermined amount of the fluctuating current potential of said source upon the grid of the tube of phaseY and amplitude to neutralize within the tube the effect o'f the uctuating current energlzation of the electrodes of said tube.

15. A system as described in claim 14 wherein the last named means includes in addition to the alternating current connection between the auxiliary electrode and the cathode a path of high impedance connected between the plate and the auxiliary electrode.

16. In a system as described in claim 14 wherein said means for impressing a predetermined amount of iiuctuating current potential upon the grid of the tube includes in addition to the alternating current coupling between the auxiliary electrode and the cathode a resistor having a value of the order of 100,000 ohms connected between the auxiliary electrode and the positive side of the source.

17. In an electrical network, a space discharge device provided with a cathode, a grid and an anode, energizing means for said device comprising a source of unidirectional current, said current having a fluctuating component, positive and negative terminals for said source, a connection including an impedance element between the negative terminal of the source and the cathode of said device, a connection between the grid and cathode of said device, said last-named connection including energy transfer means and said impedance element, a connection including energy transfer means between the anode of said device and the positive terminal of the source whereby said impedance acts to produce a bias potential for the grid of the space discharge device the magnitude of which is determined by the ow of current therethrough, a circuit connected between the source side of the last-named energy transfer means and the cathode side of said impedance, said circuit forming in eiTect a by-pass path for at least a portion of the iiuctuating component of said unidirectional current, the by-pass portion of said current passing through said impedance thereby causing a fluctuating potential to be impressed upon the grid of the discharge device, said by-pass circuit including means to determine the magnitude and phase of the by-pass uctuating component so that the fluctuating potential impressed upon the grid of said discharge device will neutralize to any desired extent the remaining fluctuating component.

BENJAMIN F. MIESSNER. 

